U.S. patent number 6,138,759 [Application Number 09/465,483] was granted by the patent office on 2000-10-31 for settable spotting fluid compositions and methods.
This patent grant is currently assigned to Halliburton Energy Services, Inc.. Invention is credited to Jiten Chatterji, Ricky A. Cox, James E. Griffith, Bryan K. Waugh.
United States Patent |
6,138,759 |
Chatterji , et al. |
October 31, 2000 |
Settable spotting fluid compositions and methods
Abstract
Improved settable spotting fluid compositions and methods are
provided. The settable spotting fluid compositions are basically
comprised of a hydraulic settable component comprised of fly ash, a
fluid loss control additive, a gel strength inhibiting additive, a
set retarding additive and water selected from the group of fresh
water and salt water present in an amount sufficient to form a
slurry having a density in the range of from about 12 to about 15
pounds per gallon.
Inventors: |
Chatterji; Jiten (Duncan,
OK), Griffith; James E. (Duncan, OK), Cox; Ricky A.
(Comanche, OK), Waugh; Bryan K. (Duncan, OK) |
Assignee: |
Halliburton Energy Services,
Inc. (Duncan, OK)
|
Family
ID: |
23847991 |
Appl.
No.: |
09/465,483 |
Filed: |
December 16, 1999 |
Current U.S.
Class: |
166/293; 166/291;
507/928; 106/708 |
Current CPC
Class: |
C04B
28/18 (20130101); C09K 8/02 (20130101); C09K
8/46 (20130101); C04B 28/021 (20130101); C09K
8/502 (20130101); C04B 28/021 (20130101); C04B
2103/22 (20130101); C04B 2103/46 (20130101); C04B
28/18 (20130101); C04B 18/08 (20130101); C04B
24/161 (20130101); C04B 24/18 (20130101); C04B
24/18 (20130101); C04B 24/383 (20130101); C04B
28/18 (20130101); C04B 14/104 (20130101); C04B
18/08 (20130101); C04B 24/161 (20130101); C04B
24/18 (20130101); C04B 24/2652 (20130101); C04B
2201/20 (20130101); Y02W 30/92 (20150501); Y10S
507/928 (20130101); Y02W 30/91 (20150501) |
Current International
Class: |
C09K
8/50 (20060101); C09K 8/42 (20060101); C09K
8/46 (20060101); C09K 8/502 (20060101); C04B
28/00 (20060101); C04B 28/18 (20060101); C04B
28/02 (20060101); C09K 8/02 (20060101); E21B
033/13 () |
Field of
Search: |
;166/291,292,293
;507/928,269 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bagnell; David
Assistant Examiner: Dougherty; Jennifer R.
Attorney, Agent or Firm: Roddy; Craig W. Dougherty, Jr.; C.
Clark
Claims
What is claimed is:
1. An improved settable spotting fluid composition for use in
cementing wells comprising:
a hydraulic settable component selected from the group consisting
of ASTM Class C or the equivalent fly ash and ASTM Class F or the
equivalent fly ash together with a source of calcium;
a fluid loss control additive;
a gel strength inhibiting additive;
a set retarding additive comprised of the calcium salt of a
sulfomethylated lignin present in said composition in an amount in
the range of from about 0.1% to about 2% by weight of said
hydraulic settable component in said composition; and
water selected from the group of fresh water and salt water present
in an amount sufficient to form a slurry having a density in the
range of from about 12 to about 15 pounds per gallon.
2. The composition of claim 1 which further comprises a free water
control additive selected from the group consisting of bentonite,
amorphous silica and hydroxyethylcellulose.
3. The composition of claim 2 wherein said free water control
additive is bentonite present in said composition in an amount in
the range of from about 1% to about 5% by weight of said hydraulic
settable component in said composition.
4. An improved settable spotting fluid composition for use in
cementing wells comprising:
a hydraulic settable component comprising ASTM Class F fly ash;
hydrated lime present in said composition in an amount of about 5%
by weight of said hydraulic settable component in said
composition;
a fluid loss control additive comprising a graft polymer having a
backbone of lignite and grafted groups of
2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile and
N,N-dimethylacrylamide or their salts present in said composition
in an amount in the range of from about 0.4% to about 0.75% by
weight of said hydraulic settable component in said
composition;
a gel strength inhibiting additive comprising a copolymer of
N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic
acid present in said composition in an amount in the range of from
about 0.4% to about 0.75% by weight of said hydraulic settable
component in said composition;
a set retarding additive comprising the calcium salt of a
sulfomethylated lignin present in said composition in an amount in
the range of from about 0.1% to about 2% by weight of said
hydraulic settable component in said composition; and
water selected from the group consisting of fresh water and salt
water present in an amount sufficient to form a slurry having a
density in the range of from about 12 to about 15 pounds per
gallon.
5. The composition of claim 4 which further comprises a free water
control additive comprised of bentonite present in said composition
in an amount in the range of from about 2% to about 5% by weight of
said hydraulic settable component in said composition.
6. An improved method of cementing a pipe string in a well bore
containing drilling fluid with a cement composition comprising the
steps of:
(a) preparing a settable spotting fluid composition comprised of a
hydraulic settable component selected from the group consisting of
ASTM Class C or the equivalent fly ash and ASTM Class F or the
equivalent fly ash together with a source of calcium, a fluid loss
control additive, a gel strength inhibiting additive, a set
retarding additive and water selected from the group of fresh water
and salt water present in an amount sufficient to form a slurry
having a density in the range of from about 12 to about 15 pounds
per gallon;
(b) pumping said settable spotting fluid composition into said well
bore to displace at least a portion of said drilling fluid out of
said well bore thereby preventing said drilling fluid from
remaining in fractures or other permeable zones in said well bore
and progressively increasing in gel strength over time therein;
(c) running said pipe string to be cemented into said well bore
whereby said pipe string and well bore are at least partially
filled with said settable spotting fluid;
(d) pumping and displacing said cement composition through said
pipe string and into the annulus between said pipe string and the
walls of said well bore whereby said drilling fluid and said
settable spotting fluid
composition in said pipe string and said annulus are displaced
therefrom except for portions of said settable spotting fluid
composition which may remain in fractures or other permeable zones
therein; and
(e) allowing said cement composition in said annulus and any
settable spotting fluid composition remaining in said fractures or
other permeable zones therein to set into hard impermeable masses
therein.
7. The method of claim 6 wherein said hydraulic settable component
in said settable spotting fluid composition is ASTM Class F or the
equivalent fly ash together with a source of calcium.
8. The method of claim 7 wherein said source of calcium in said
settable spotting fluid composition is lime.
9. The method of claim 6 wherein said fluid loss control additive
in said settable spotting fluid composition is selected from the
group consisting of a graft polymer having a backbone selected from
the group consisting of lignin, lignite and their salts and at
least one grafted group of 2-acrylamido-2-methylpropanesulfonic
acid, acrylonitrile and N,N-dimethylacrylamide or their salts and a
random polymerization product of two or three different vinyl
containing monomers including a vinylamide morpholine
derivative.
10. The method of claim 6 wherein said fluid loss control additive
in said settable spotting fluid composition is a graft polymer
having a backbone of lignite and grafted groups of
2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile and
N,N-dimethylacrylamide or their salts and is present in said
composition in an amount in the range of from about 0.1% to about
1% by weight of said hydraulic settable component in said
composition.
11. The method of claim 6 wherein said gel strength inhibiting
additive in said settable spotting fluid composition is selected
from the group consisting of copolymers and copolymer salts of
N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic
acid and is present in said composition in an amount in the range
of from about 0.1% to about 1% by weight of said hydraulic settable
component in said composition.
12. The method of claim 6 wherein said set retarding additive in
said settable spotting fluid composition is selected from the group
consisting of the ammonium, alkali metal, alkaline earth metal and
other metal salts of a sulfoalkylated lignin.
13. The method of claim 6 wherein said set retarding additive in
said settable spotting fluid composition is the calcium salt of a
sulfomethylated lignin and is present in said composition in an
amount in the range of from about 0.1% to about 2% by weight of
said hydraulic settable component in said composition.
14. The method of claim 6 wherein said composition further
comprises a free water control additive selected from the group
consisting of bentonite, amorphous silica and hydroxyethyl
cellulose.
15. The method of claim 14 wherein said free water control additive
is bentonite present in said composition in an amount in the range
of from about 1% to about 5% by weight of said hydraulic settable
component in said composition.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to settable spotting fluid compositions and
methods of using the compositions in cementing wells.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in the
construction of oil and gas wells. For example, hydraulic cement
compositions are used in primary cementing operations whereby
strings of pipe such as casings and liners are cemented in well
bores. In performing primary cementing, a hydraulic cement
composition is pumped into the annular space between the walls of a
well bore and the exterior surfaces of a pipe string disposed
therein. The cement composition is permitted to set in the annular
space thereby forming an annular sheath of hardened substantially
impermeable cement therein. The cement sheath physically supports
and positions the pipe string in the well bore and bonds the
exterior surfaces of the pipe string to the walls of the well bore
whereby the undesirable migration of fluids between zones or
formations penetrated by the well bore is prevented.
A variety of drilling fluids are used in drilling wells. The most
commonly used drilling fluids are solids containing water base gels
which can be weighted with particulate weighting material such as
barite. During the drilling of a well bore, the drilling fluid used
is circulated through the drill pipe and drill bit and then
upwardly through the well bore to the surface. The drilling fluid
functions to lubricate the drill bit and carry cuttings to the
surface where the cuttings and gas are removed from the drilling
fluid. While drilling fluids are not settable, i.e., they do not
set into hard impermeable sealing masses when static, drilling
fluids increase in gel strength over time. Typically, after a well
bore is drilled to total depth, the drill pipe and drill bit are
withdrawn from the well bore and the drilling fluid is left in the
well bore to provide hydrostatic pressure on permeable formations
penetrated by the well bore thereby preventing the flow of
formation fluids into the well bore.
The next operation in completing the well bore usually involves
running a pipe string, e.g., casing, into the well bore. Depending
upon the depth of the well bore and whether or not problems are
encountered in running the pipe string therein, the drilling fluid
may remain relatively static in the well bore for a time period up
to 2 weeks. During that time, the stagnate drilling fluid
progressively increases in gel strength whereby the portions of the
drilling fluid in the well bore become increasingly difficult to
displace.
After the pipe string has been run in the well bore, the next
operation performed is usually primary cementing. That is, the pipe
string disposed in the well bore is cemented by pumping a cement
composition through the pipe string and into the annulus between
the pipe string and the walls of the well bore whereby the drilling
fluid in the annulus is displaced therefrom by the cement
composition. While a variety of techniques have been developed for
improving the displacement of the drilling fluid from the annulus,
if the drilling fluid has developed gel strength due to remaining
static in the well bore for a long period of time, the portions of
the drilling fluid in the well bore are bypassed by the cement
composition. Since the drilling fluid is not settable, i.e., it
does not set into a rigid enough mass to resist entry and flow of
formation fluids in the well bore, formation fluids enter and flow
in the well bore which is highly undesirable.
Heretofore, settable spotting fluid compositions have been
developed and used in wells for various purposes including the
early displacement of drilling fluids from well bores. However, the
prior settable spotting fluids have included blast furnace slag and
other hydraulic components which slowly set at relatively low
temperatures, i.e., temperatures less than about 90.degree. F.
Also, slag-containing settable spotting fluids are intolerant to
cement composition contamination, i.e., if well cement mixes with
such spotting fluids, the spotting fluids prematurely set. To
prevent a slag-containing spotting fluid from prematurely setting,
a very strong set retarder must be added to the spotting fluid and
the spotting fluid must be separated from the cement composition by
a spacer fluid. If intermixing between the cement composition and
the set retarded spotting fluid occurs, the cement composition may
be prevented from setting by the strong set retarder in the
spotting fluid.
Thus, there are needs for improved settable spotting fluid
compositions which can be utilized to avoid well cementing problems
of the types described above at subterranean temperatures above
90.degree. F.
SUMMARY OF THE INVENTION
By the present invention improved settable spotting fluid
compositions and methods of using the compositions in well
cementing at temperatures up to about 150.degree. F. are provided
which meet the above described needs and overcome the deficiencies
of the prior art. The settable spotting fluid compositions of this
invention are basically comprised of a hydraulic settable component
selected from ASTM Class C or the equivalent fly ash or ASTM Class
F or the equivalent fly ash together with a source of calcium, a
fluid loss control additive, a gel strength inhibiting additive, a
set retarding additive and water selected from the group of fresh
water and salt water present in an amount sufficient to form a
slurry having a density in the range of from about 12 to about 15
pounds per gallon. When the amount of water required in a settable
spotting fluid composition of this invention to achieve a desired
density produces free water in the composition, a free water
control agent such as bentonite, amorphous silica or
hydroxyethylcellulose can be included in the composition to convert
the free water to a gel.
Because the settable spotting fluid compositions of this invention
are tolerant to well cement contamination, excessive or very strong
set retarders do not need to be included in the compositions.
Further, when displacing a settable spotting fluid composition of
this invention with a well cement composition, a spacer fluid
between the spotting fluid composition and the well cement
composition does not have to be utilized, and there is no need to
utilize a spacer for improving the settable spotting fluid
displacement since any bypassed settable spotting fluid will set
with time.
The improved methods of this invention for cementing a pipe string
such as casing in a well bore containing drilling fluid with a
cement composition are basically comprised of the steps of
preparing a settable spotting fluid composition of this invention,
pumping the settable spotting fluid composition into the well bore
to displace at least a portion of the drilling fluid from the well
bore thereby preventing the drilling fluid from remaining in the
well bore and progressively increasing in gel strength over time
therein, running the pipe string to be cemented into the well bore
whereby the pipe string and well bore are at least partially filled
with the settable spotting fluid, pumping and displacing the cement
composition through the pipe string and into the annulus between
the pipe string and the walls of the well bore whereby the drilling
fluid and the settable spotting fluid composition in the pipe
string and in the annulus are displaced therefrom except for
portions of the settable spotting fluid composition which may
remain in fractures or other permeable zones in the well bore, and
allowing the cementing composition in the annulus and any settable
spotting fluid composition remaining in the fractures or other
permeable zones to set into a hard impermeable mass therein.
It is, therefore, a general object of the present invention to
provide improved settable spotting fluid compositions and methods
of using the compositions in cementing wells.
Other and further objects, features and advantages of the present
invention will be readily apparent to those skilled in the art upon
a reading of the description of preferred embodiments which
follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
The improved settable spotting fluid compositions of this invention
for use in cementing wells at temperatures up to about 150.degree.
F. are basically comprised of a hydraulic settable component
selected from ASTM Class C or the equivalent fly ash or ASTM Class
F or the equivalent fly ash together with a source of calcium, a
fluid loss control additive for preventing the loss of water from
the composition to permeable subterranean formations, a gel
strength inhibiting additive for preventing the composition from
gaining gel strength for an initial relatively long period of time,
a set retarding additive for delaying the setting of the
composition into a hard impermeable mass for a relatively long
period of time and water selected from the group of fresh water and
salt water present in an amount sufficient to form a slurry having
a density in the range of from about 12 to about 15 pounds per
gallon.
The term "settable spotting fluid composition(s)" is used herein to
mean a fluid which over time will harden into an impermeable mass
having sufficient compressive strength to prevent the undesirable
entry into and the flow of formation fluids in the well bore, but
which will not set for a desired relatively long period of time in
the range of from about 2 days to about 2 weeks or more. During
this time, a pipe string, e.g., casing, can be placed in the well
bore and conventional cementing operations can be completed.
Fly ash is produced by the combustion of powdered coal with a
forced draft. The fly ash which is carried by the flue gases is
recovered, for example, by electrostatic precipitators. ASTM Class
C or the equivalent fly ash contains both silica and lime and when
mixed with water forms a cementitious mixture which sets into a
hard impermeable mass, i.e., calcium silicate hydrate. Class F fly
ash does not contain lime, and a source of calcium ion is required
for it to form a cementitious composition with water. Generally,
lime is mixed with Class F or the equivalent fly ash in an amount
in the range of from about 0% to about 25% by weight of the fly
ash. Of the two forms of fly ash which are commercially available,
i.e., ASTM Class C or ASTM Class F, ASTM Class F together with lime
is preferred for use in accordance with the present invention.
A variety of fluid loss control additives can be used in accordance
with this invention which are well known to those skilled in the
art. A preferred such fluid loss control additive is a graft
polymer having a backbone selected from the group consisting of
lignin, lignite and their salts and grafted groups of at least one
of 2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile or
N,N-dimethylacrylamide or their salts. The above described fluid
loss additives are disclosed in detail in U.S. Pat. No. 4,676,317
issued to Fry et al. on Jun. 30, 1987, which is incorporated herein
by reference. Another preferred fluid loss control additive for use
in accordance with the present invention is a random polymerization
product of two or three different vinyl containing monomers
including a vinyl amide morpholine derivative. Such a fluid loss
control additive is disclosed in detail in U.S. Pat. No. 5,988,279
issued to Udarbe et al. on Nov. 23, 1999, which is incorporated
herein by reference. Of the above described fluid loss control
additives, a graft polymer having a backbone of lignite and grafted
groups of 2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile
and N,N-dimethylacrylamide or their salts is most preferred. The
fluid loss control additive utilized is included in an improved
settable spotting fluid composition of this invention in the
general amount of from about 0.1% to about 1% by weight of the
hydraulic settable component in the settable spotting fluid
composition, more preferably in an amount in the range of from
about 0.4% to about 0.75%.
The gel strength inhibiting additives useful in accordance with
this invention which also function to reduce fluid loss are
preferably selected from copolymers and copolymer salts of
N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic
acid. These fluid loss additives are disclosed in detail in U.S.
Pat. No. 4,555,269 issued to Rao et al. on Nov. 26, 1985, which is
incorporated herein by reference. The gel strength inhibiting
additive used is generally included in a settable spotting fluid
composition of this invention in an amount in the range of from
about 0.1% to about 1% by weight of the hydraulic settable
component in the composition, more preferably in an amount in the
range of from about 0.4% to about 0.75%.
The set retarding additive is preferably selected from the
ammonium, alkali metal, alkaline earth metal or other metal salts
of a sulfoalkylated lignin. Such set retarding additives are
disclosed in detail in U.S. Pat. No. Re. 31,190 reissued to Detroit
et al. on Mar. 29, 1983, which is incorporated herein by reference.
The most preferred set retarding additive of this type is the
calcium salt of a sulfomethylated lignin. The set retarding
additive is included in a settable spotting fluid composition of
this invention in an amount in the range of from about 0.1% to
about 2% by weight of the hydraulic settable component in the
composition.
As mentioned, the water utilized in the settable spotting fluid
compositions of this invention can be fresh water or salt water
depending upon the particular density of the composition required.
The term "salt water" is used herein to mean unsaturated salt water
or saturated salt water including brines and seawater. The water is
included in the settable spotting fluid compositions in an amount
sufficient to form a slurry having a density in the range of from
about 12 to about 15 pounds per gallon.
In order to prevent the presence of free water in the settable
spotting fluid compositions, a free water control additive selected
from bentonite, amorphous silica and hydroxyethylcellulose can be
included in the compositions. Of the foregoing free water control
additives, bentonite is preferred. When used, the free water
control additive is present in the compositions of this invention
in an amount in the range of from about 1% to about 5% by weight of
the hydraulic settable component in the compositions.
The most preferred settable spotting fluid composition of this
invention is comprised of a hydraulic settable component comprising
ASTM Class F or the equivalent fly ash; hydrated lime present in
the composition in an amount of about 5% by weight of the hydraulic
settable component in the composition; a fluid loss control
additive comprising a graft polymer having a backbone of lignite
and grafted groups of
2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile and
N,N-dimethylacrylamide or their salts present in the composition in
an amount in the range of from about 0.4% to about 0.75% by weight
of the hydraulic settable component in the composition; a gel
strength inhibiting additive comprising a copolymer of
N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic
acid present in the composition in an amount in the range of from
about 0.4% to about 0.75% by weight of the hydraulic settable
component in the composition; a set retarding additive comprising
the calcium salt of a sulfomethylated lignin present in the
composition in an amount in the range of from about 0.1% to about
2% by weight of the hydraulic settable component in the
composition; and water selected from the group consisting of fresh
water and salt water present in an amount sufficient to form a
slurry having a density in the range of from about 12 to about 15
pounds per gallon.
The above composition can also include a free water control
additive comprised of bentonite present in the composition in an
amount in the range of from about 2% to about 5% by weight of the
hydraulic settable component in the composition.
In accordance with the methods of the present invention, when a
well bore is drilled to total depth and before the drilling fluid
in the well bore has had a chance to gain significant gel strength,
the drilling fluid is at least partially displaced with an improved
settable spotting fluid composition of this invention. The drilling
fluid is usually displaced by the settable spotting fluid
composition to a level above those portions of the well bore
containing fractures, vugs and other permeable areas or zones. The
spotting fluid composition does not increase in gel strength with
time like the drilling fluid, and it is easily displaced after
being static in the well bore for a long period of time, e.g., a
time period up to about two weeks. Because the drilling fluid has
not had a chance to increase in gel strength and because the drill
pipe includes large diameter drill collars and the like which cause
high annular velocity, displacement of the drilling fluid is
achieved by the settable spotting fluid composition of this
invention.
After the well bore is at least partially filled with the spotting
fluid composition, the pipe string to be cemented is run in the
well bore. Depending on how much of the drilling fluid has
previously been displaced, and if the pipe string is not floated
into the well bore while being filled with the spotting fluid
composition, some drilling fluid will remain in the pipe string.
When the well cement composition is pumped through the pipe string
into the annulus, the drilling fluid and spotting fluid composition
in the pipe string and annulus are displaced ahead of the well
cement composition. Because the annulus contains the spotting fluid
composition, any drilling fluid entering the annulus will not have
time to increase in gel strength therein and will be readily
displaced therefrom by the well cement composition. The settable
spotting fluid composition, if any, remaining in fractures or other
permeable areas or zones in the well bore will ultimately set
thereby preventing the entry or flow of formation fluids in the
annulus.
Thus, the improved methods of this invention for cementing a pipe
string in a well bore containing drilling fluid with a well cement
composition are basically comprised of the following steps: (a)
preparing a settable spotting fluid composition of this invention;
(b) pumping the settable spotting fluid composition into the well
bore to displace at least a portion of the drilling fluid out of
the well bore thereby preventing the drilling fluid from remaining
in fractures or other permeable zones in the well bore and
progressively increasing in gel strength over time therein; (c)
running the pipe string to be cemented into the well bore whereby
the pipe string and well bore are at least partially filled with
the settable spotting fluid; (d) pumping and displacing the well
cement composition through the pipe string and into the annulus
between the pipe string and the walls of the well bore whereby the
drilling fluid and the settable spotting fluid composition in the
pipe string and the annulus are displaced therefrom except for
portions of the settable spotting fluid composition which may
remain in fractures or other permeable zones therein; and (e)
allowing the well cement composition in the annulus and any
settable spotting fluid composition remaining in the fractures or
other permeable zones therein to set into hard impermeable masses
therein.
In order to further illustrate the compositions and methods of the
present invention, the following example is given.
EXAMPLE
A base settable spotting fluid without additives was prepared
comprised of 74 pounds of ASTM Class F fly ash, 3.7 pounds of lime
(5% by weight of the fly ash) and 4.59 gallons of synthetic
seawater. The resulting slurry had a density of 13.8 pounds per
gallon. A fluid loss control additive, a gel strength inhibiting
additive and a set retarding additive were added to first and
second test portions of the base slurry in different amounts. A
free water control agent was also added to the first portion. The
rheologies of the first and second test portions were determined
utilizing a Fann viscometer in accordance with the standard testing
procedures set forth in API Specification For Material And Testing
For Well Cements, API RP 10B, 21.sup.st Edition dated Sep. 1, 1991,
of the American Petroleum Institute, Washington, D.C. The test
settable spotting fluid compositions and the test results are set
forth in Table I below.
TABLE I
__________________________________________________________________________
Settable Spotting Fluid Compositions And Rheologies Quantities of
Additives in Base Composition Fluid Loss Gel Strength Set Retarding
Free Water Control Inhibiting Additive.sup.3, % Control Fann
Viscometer Readings, Bc Composition Additive.sup.1, % by
Additive.sup.2, % by by wt. of Fly Additive.sup.4, % by 100 200 300
200 100 6 3 No. wt. of Fly Ash wt. of Fly Ash Ash wt. of Fly Ash
rpm rpm rpm rpm rpm rpm rpm
__________________________________________________________________________
1 1.0 0.42 0.6 5 20 34 48 34 20 8 7 2 0.5 0.5 0.6 -- 36 61 84 60 36
10 8
__________________________________________________________________________
.sup.1 A graft copolymer having a backbone of lignite and grafted
groups of 2acrylamido-2-methylpropanesulfonic acid, acrylonitrile
and N,Ndimethylacrylamide .sup.2 Copolymer salt of
N,Ndimethylacrylamide and 2acrylamido-2-methylpropanesulfonic acid
.sup.3 Calcium salt of a sulfomethylated lignin .sup.4
Bentonite
From Table I, it can be seen that the settable spotting fluid
compositions tested had good rheologies for functioning as
displacement fluids.
The settable spotting fluid compositions given in Table I were
tested for gel strength at 80.degree. F. over time, fluid loss at
80.degree. F. and set time at 150.degree. F. The results of these
tests are set forth in Table II below.
TABLE II
__________________________________________________________________________
Quantities of Additives in Base Composition Fluid Loss Gel Strength
Fluid Set Control Inhibiting Set Retarding Free Water Control Loss
Time @ Composition Additive.sup.1, % by Additive.sup.2, % by
Additive.sup.3, % by Additive.sup.4, % by Gel Strength @ 80.degree.
80.degree. F., 150.degree. F., No. wt. of Fly Ash wt. of Fly Ash
wt. of Fly Ash wt. of Fly Ash 0 sec. 10 min. 30 min. cc days
__________________________________________________________________________
1 1.0 0.42 0.6 5 7 9 8 7.4 11 2 0.5 0.5 0.6 -- 8 9 10 7 11
__________________________________________________________________________
.sup.1 A graft copolymer having a backbone of lignite and grafted
groups of 2acrylamido-2-methylpropanesulfonic acid, acrylonitrile
and N,Ndimethylacrylamide .sup.2 Copolymer salt of
N,Ndimethylacrylamide and 2acrylamido-2-methylpropanesulfonic acid
.sup.3 Calcium salt of a sulfomethylated lignin .sup.4
Bentonite
From Table II it can be seen that the gel strengths of the test
settable spotting fluid compositions remained stable, the
compositions had low fluid loss and the compositions did not set
for 11 days.
Thus, the present invention is well adapted to attain the objects
and advantages mentioned as well as those which are inherent
therein. While numerous changes may be made by those skilled in the
art, such changes are encompassed within the spirit of this
invention as defined by the appended claims.
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